The present invention relates to magnetic recording media, such as thin film magnetic recording disks, and to a method of manufacturing the media. The present invention has particular applicable to high areal density longitudinal magnetic recording media exhibiting low noise and enhanced magnetic performance.
Magnetic recording media are extensively employed in the computer industry and can be locally magnetized by a write transducer or write head to record and store information. The write transducer creates a highly concentrated magnetic field which alternates direction based upon bits of the information being stored. When the local magnetic field produced by the write transducer is greater than the coercivity of the recording medium, grains of the recording medium at that location are magnetized. The grains retain their magnetization after the magnetic field produced by the write transducer is removed. The direction of the magnetization matches the direction of the applied magnetic field. The magnetization of the recording medium can subsequently produce an electrical response to a read sensor, allowing the stored information to be read.
There is an ever increasing demand for magnetic recording media with higher storage capacity, lower noise and lower costs. Efforts, therefore, have been made to reduce the size required to magnetically record bits of information, while maintaining the integrity of the information as size is decreased. The space necessary to record information in magnetic recording media depends upon the size of transitions between oppositely magnetized areas. It is, therefore, desirable to produce magnetic recording media that will support the smallest transition size possible. However, the signal output from the transition must avoid excessive noise to reliably maintain the integrity of the stored information. Media noise is generally characterized as the sharpness of a signal on readback against the sharpness of a signal on writing and is generally expressed in signal-to-media noise ratio (SMNR).
The increasing demands for higher areal recording density impose increasingly greater demands on thin film magnetic recording media in terms of remanent coercivity (Hr), magnetic remanance (Mr), coercivity squareness (S*), SMNR, and narrow track recording performance. It is extremely difficult to produce a magnetic recording medium satisfying such demanding requirements.
The linear recording density can be increased by increasing the Hr of the magnetic recording medium, and can be accomplished by decreasing the medium noise, as by maintaining very fine magnetically non-coupled grains. Medium noise in thin films is a dominant factor restricting increased recording density of high density magnetic hard disk drives, and is attributed primarily to inhomogeneous and large grain size and intergranular exchange coupling. Accordingly, in order to continually increase linear density, medium noise must be minimized by suitable microstructure control.
Longitudinal magnetic recording media containing cobalt (Co) or a Co-based alloy magnetic films with a chromium (Cr) or Cr alloy underlayer deposited on a nonmagnetic substrate have become the industry standard. For thin film longitudinal magnetic recording media, the desired crystallized structure of the Co and Co alloys is hexagonal close packed (HCP) with uniaxial crystalline anisotropy and a magnetization easy direction along the c-axis is in the plane of the film. The better the in-plane c-axis crystallographic texture, the more suitable is the Co alloy thin film for use in longitudinal recording to achieve high remanance. For very small grain sizes coercivity increases with increased grain size. The large grains, however, result in greater noise. Accordingly, there is a need to achieve high coercivities without the increase in noise associated with large grains. In order to achieve low noise magnetic recording media, the Co alloy thin film should have uniform small grains with grain boundaries capable of magnetically isolating neighboring grains. In other words, in order to continually increase recording density, the magnetic grain size and grain size distribution must be decreased. A small magnetic grain size and small grain size distribution will lead to decreased media noise and improved thermal stability. The magnetic grain size is affected by the substrate surface condition, and processing conditions such as substrate temperature, bias voltage, underlayer alloys and magnetic alloys. Microstructural and crystallographic control is typically attempted by manipulating the deposition process, grooving the substrate surface and proper use of an underlayer.
Underlayers can strongly influence the crystallographic orientation, grain size and chemical segregation of the Co alloy grain boundaries. Conventional underlayers include Cr and alloys of Cr with elements such as titanium (Ti), tungsten (W), molybdenum (Mo) and vanadium (V).
It is recognized that magnetic properties, such as Hr. Mr, S* and SMNR, which are critical to the performance of a magnetic alloy film, depend primarily upon the microstructure of the magnetic layer which, in turn, is influenced by the underlying layers, such as the underlayer. It is also recognized that underlayers having a fine grain structure are highly desirable, particular for growing fine grains of HCP Co alloys deposited thereon.
In copending U.S. patent application Ser. No. 09/382,581, now U.S. Pat. No. 6348276, filed on Aug. 25, 1999 a magnetic recording medium is disclosed comprising a surface-oxidized nickel-aluminum (NiAl) sub-seedlayer, a NiAl seedlayer, a Cr-alloy underlayer, an intermediate CoCrTa alloy, a magnetic layer and a carbon-containing protective overcoat.
In copending U.S. patent application Ser. No. 09/152,326 filed on Sep. 14, 1998, now U.S. Pat. No. 6117570, filed on Sep. 14, 1998 a magnetic recording medium is disclosed comprising a NiAl seedlayer having an oxidized surface, a chromium underlayer on the seedlayer, and a magnetic layer of the underlayer.
Okumura et al. in U.S. Pat. No. 5,480,733 disclose a magnetic recording medium comprising an NiPxe2x80x94X laminated on a nonmetallic substrate with sequentially formed Cr underlayer, magnetic recording layer and protection layer thereon, wherein X is one or more elements belonging to group 4, 5 and 6 of the periodic table. Zhang in U.S. Pat. No. 5,858,566 discloses a magnetic recording medium comprising a NiAl seedlayer, a Cr underlayer and a Co magnetic layer. Ataka et al. in U.S. Pat. No. 5,939,202 disclose a magnetic recording medium comprising a non-magnetic substrate, non-magnetic base layer, magnetic layer and protective layer, wherein the non-magnetic metal base layer contains NiAl to which at least one of tungsten (W), tantalum (Ta), hafnium (Hf), molybdenum (Mo), Cr, zirconium (Zr) and niobium (Nb) is added.
Okumura et al. in U.S. Pat. No. 5,700,593 disclose a magnetic recording medium comprising a substrate and a seedlayer comprising an oxygen-containing non-magnetic amorphous metal or a seedlayer comprising a non-magnetic amorphous metal having an oxygen-containing layer thereon, and an underlying non-magnetic layer laminated on the seedlayer. Doerner et al. in U.S. Pat. No. 5,302,434 disclose a magnetic recording medium comprising an untextured nickel phosphorous coating on a disk substrate which is oxidized to form a nickel oxide film. Suzuki et al. in U.S. Pat. No. 5,587,234 disclose a magnetic recording medium comprising a multi-layer structure containing at least one paramagnetic intermediate region or oxygen-rich region disposed between magnet layers. Chen et al. in U.S. Pat. No. 5,866,227 disclose a magnetic recording medium comprising a glass or glass-ceramic substrate formed by sequentially depositing thereon a partially oxidized nickel phosphorous seedlayer, an underlayer and a magnetic layer. Chen et al. in U.S. Pat. No. 6,010,795 disclose a magnetic recording medium comprising a surface oxidized NiP seedlayer, a Cr-containing subunderlayer, a NiAl or FeAl underlayer, Cr-containing intermediate layer and magnetic layer. Takahashi in U.S. Pat. No. 6,042,939 discloses a magnetic recording medium comprising an oxidized NiP layer.
There exists a continuing need for high areal density longitudinal magnetic recording media exhibiting high Hr and high SMNR, and methodology for manufacturing such magnetic recording media. There also exist a need for magnetic recording media containing a glass or glass-ceramic substrate exhibiting high Hr and high SMNR.
An advantage of the present invention is a magnetic recording medium for high areal recording density exhibiting low noise and high Hr.
Another advantage of the present invention is a method of manufacturing a magnetic recording medium suitable for high areal recording density and exhibiting low noise and high Hr.
Additional advantages and features of the present invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following only to be learned from the practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to the present invention, the foregoing and other advantages are achieved by a magnetic recording medium comprising a non-magnetic substrate; a seedlayer comprising: oxidized nickel phosphorous (NiP) containing at least one dopant element (X) having an oxidation potential greater than that of NiP; or oxidized nickel aluminum (NiAl) containing at least one dopant element (Y) having an oxidation potential greater than that of NiAl; and a magnetic layer.
Another aspect of the present invention is a method of manufacturing a magnetic recording medium, the method comprising depositing a seedlayer comprising: nickel phosphorous (NiP) containing at least one dopant element (X) having an oxidation potential greater than that of NiP; or nickel aluminum (NiAl) containing at least one dopant element (Y) having an oxidation potential greater than that of NiAl; oxidizing the seedlayer and at least one dopant element (X) or (Y); and depositing a magnetic layer.
Embodiments of the present invention comprise magnetic recording media having oxidized seedlayers wherein the dopant elements (X) and (Y) have an oxidation potential greater than xe2x88x920.10 volts and are present in the seedlayer in a total amount of about 200 ppm to about 5 at. % such that, upon oxidation, the seedlayer comprises about 50 to about 500 ppm of oxygen and the magnetic layer has a grain size less than about 10 nm and a uniform grain size distribution with a standard deviation less than about 2 nm.
Embodiments of the present invention further comprise sputter depositing the seedlayer in an oxygen-containing environment to directly deposit an oxidized seedlayer or depositing a NiP or NiAl layer, ion etching the deposited layer, oxidizing the seedlayer in an atmosphere containing about 5 to about 30 vol. % oxygen and then sequentially depositing a Cr or Cr-alloy underlayer, a Coxe2x80x94Cr intermediate layer, a magnetic layer and a carbon-containing protective overcoat.
Additional advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the present invention is shown and described, simply by way of illustration of the best mode contemplated for carrying out the present invention. As will be realized, the present invention is capable of other and different embodiments, and its details are capable of modifications in various obvious respects, all without departing from the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not as restrictive.